Hey Guys, Anyone Tell Me How I Can Check My A/c Compressor On My 69 . The System Needs To Be Charged And I Would Like To Find Out If The Compreeor Will Kick On . Just Bought The Car A Few Months Ago And The Previos Owner Said He Had Not Tried The A/C In Years. I Do Know That You Have To Have The A/C Charged To Work But I Thought There Might Be A Way To Cross Some Wires To See If The Comprssor Will Work Before I Go Threw The Recharge Prosess. Thnx Dave.

 

Well, the basics are the controll panel will just toss 12 volts to the compressor solenoid coil, and that should click on and allow the very front of the compressor to spin with the belt driven pulley i'ts now engaged to, i'ts a system that's allways on, meaning, you have two valves in the system that regulate how much and where the freon is supposed to be, sometimes there was a limit switch in the rear of the compressors to actually blow the fuse feeding the 12 volts to the coil, this right next to the compressor, under the hood, looks like some crazy wiring, so first thing is to hit that coil with 12 volts and see if it's running along with engine,...
second off is hook up some gauges, and find out what if any pressure readings are.....
then toss in some air pressure, to see if it holds air, I do that off my shop air line, 125 lbs or so, then shut off the air feed, and monitor any leakage.....this before bothering with any pull down with vacuum pump...

GENE

 

I would make sure you have a sealed system first. Go to either the high or low side fitting and press on the valve for a second to see if any freon is in the system. If there is I would then hook up R-12 gauges to check the readings in the system. Usually a good reading will be the low side at 35-40 and the high side between 150-200. When you turn the A/C on power will be sent to the compressor and it should kick on if their is freon in the system. The compressor needs to kick on to get a reading in your gauges if freon is present. If I remember correctly your car could have a thermo limiter in the line but it may be the a/c system that doesn't require one like in one of my other collector cars my 70' Monte Carlo. This fuse will blow out if the freon leaks out or if a slow leak over the years made your system become low on freon. It is a 3 prong little plastic plug-in. Look to see if there is one in your a/c wiring harness. If you have one and it blew you need to change it for the compressor to kick on. I see where another member told you to pump air into the system to check for a leak if you find no freon in the system. I don't agree with that because if your dryer is still good after introducing air into the system it will suck every bit of moisture out of that air and be destroyed from doing this. A vacuum pump is required to do this properly. You need to hook one up and vaccum the system down for at least 15 minutes and if the low side gauge holds vacuum which you will see when viewing your R-12 gauges the sytem has no leak and if it doesn't you have a leak simple as that. If you have a leak and want to find it yourself the cheapest thing to do is to go out and find the product Freeze 12 at one of your local part stores in 12 oz cans. This product is the closes thing to R-12 Freon and can be introduced right into the R-12 system. Being in the automotive parts business 27 years now I have sold this product to repair garages that have been using this freon for a number of years and swear by it. They rather use Freeze 12 then retrofit to R134A. It will suck right into the system without having to run the compressor after you vacumm the sytem if you don't have any leaks. If you have a leak and want to find it the only way you will be able to do this is to put freeze 12 into the system but you will need to start the car and by pass the power to the compressor so that it will pull the new freon in while the engine is running. On later GM cars this can be done with a paper clip. I am not exactly sure what you will need to do to bypass the system on your 69' maybe someone can weight in that knows for sure. Good Luck.

Fred

 

Fred is right on. Gauges are a must. The pressures Fred gave are with the system running and the compressor engaged.

You will need gauges to check the system. I would hook up the gauges with everything off and see if there is any pressure. IF there is pressure,, no air has leaked into the system. Then I would turn the compressor by hand to see if it is frozen up. Next I would put 12 V to the clutch to see if it would engage. Then if it does engage, with the gauges on,, start the car and watch the gauges. If the high side goes up and the low side goes down the compressor is working. Warning. you don't want to go negative on the low side because this will pull air into the system through a leak. IF the compressor runs and pressures work as described. Turn it off, then you can add freon to the system through the gauges. You might have to put the 12 V on the compressor to get the freon into the system. Add about 1 # of freon,, shut the system down and check for leaks.

If you find no leakage then you can proceed to add more freon.
When the low side pressure is high enough (28 psi if I remember correctly),, you can remove the 12 V jumper and use the car a/c power plug. Then add freon until the pressure is in the 200 - 220 range on the high side and the low side is about 30 - 32 depending on the compressor condition.

IF you have no leaks the system will continue to function.

You must use caution and not to vent freon to the atmosphere or be injured. Liquid freon can do instant freeze damage.

So be careful and good luck. 99 Nassau Blue

 

I couldn't of said it any better.

 

thnx guys. where do i hook up the freon hose to charge the system??

 

On the low side. Are you doing this with a set of R-12 gauges or are you just going out and getting one of those cheap single hose setups to put freon in without gauges? If you are be careful because you are not going to be able to see what is happening on the high and low side of the a/c system by not using a set of R-12 gauges. If you put to much freon in you will have a problem also. If you go the cheap route the only thing you have going for you is to make sure and locate the site glass usually sitting right on top of the dryer or in one of the refrigerant lines and check for bubbles. If there are bubbles your a/c system is in need of freon. Only put enough in until the bubbles stop showing and then disconnect the freon hose from the low side. You have to have the car running and the air conditioning on to do this procedure.

 

is the low side valve one of the fittings on the back of the compressor ?? i see two fittings on the back end of the compressor. i also see a fitting on a valve on the passenger side , between the engine and the fender ??

 

On a 69 there are no high or low pressure limit switches or fuses. If you turn on the system from the console in the car the compressor clutch should engage regardless of the amount of R-12 in the system. If the clutch is not engaging then you have other issues with the system that will need to be addressed before you charge it.

Regards,

Jay

 

You never answered any of my questions to you. With a set of R-12 gauges you will be able to tell right away what is what as far as your fittings are concerned. The high side fitting is always smaller then the low side fitting in your GM a/c system.

 

If all you want to do is see if the compressor will physically rotate, just grab it on the end and try to rotate it by hand (WITH ENGINE OFF OF COURSE!!!) A good one will rotate for you. Next step could be to jumper 12v to the fan clutch solenoid - find the two-wire connector that plugs in right by the pulley. With car running, when you jumper those leads, the clutch should engage and start spinning the whole front and not just the pulley. Caution - if system is discharged/not sealed anymore you are now pushing air, moisture and possibly other crap through that compressor. Therefore only try the jumper for a second or two... At this point, your curiosity should be satisfied about the function of your compressor. You'll want to do the guages, freon, etc. as advised - or take it to an a/c pro.

 

how much freon does a 75 system hold? Copmpletly bone dry fresh from a restore.

 

About 3-3-1/2 (12oz cans).

 

what have you been charged for a recharge or complete fill?